This application claims priority from Japanese Patent Application Reference No. 2000-045085, filed Feb. 17, 2000, the entire content of which is incorporated herein by reference for all purposes.
The present invention relates generally to a storage apparatus used for computer systems, and specifically to the storage apparatus, which can be connected to computers by a plurality of kinds of interfaces.
Conventionally, a small computer such as a personal computer (PC) or a workstation can be used for the jobs formerly handled by a large so-called mainframe computers. Accordingly, there are some computer systems comprising a mixture of mainframes, PCs and workstations using different kinds of computers and operating systems.
Disk subsystems can be used in these kinds of computer systems. For example, a disk subsystem currently in use comprises I/O interfaces of a Count Key Data format (CKD format), generally used in a mainframe, and a Fixed-Block Length format, typically used in a small computer such as a PC or workstation. In such kinds of disk subsystems, if the host computer is connected with CKD format interfaces, the disk subsystem transfers data to the host computer after converting the data into CKD format. Analogously, when the host computer is connected with Fixed-Block Length format interface, the disk subsystem transfers data to the host computer after converting the data into Fixed-Block Length format. By using such techniques, it becomes possible for the host computers with different I/O interfaces to share the data between them. What is really needed are techniques to increase data transfer performance during read or write of the data stored in Fixed-Block Length format in computer configurations in which a plurality of host computers are connected by a CKD format interface to a disk subsystem.
According to the invention, techniques for increasing data transfer performance during read or write of data stored in Fixed-Block Length format are provided. The present invention can be embodied in computer configurations in which a plurality of host computers are connected by a CKD format interface to a disk subsystem, for example. Specific embodiments include systems, apparatuses and methods. Such specific embodiments can provide increased data transfer performance in multiple format disk drive subsystems.
In a representative embodiment according to the present invention, an access method for use with a storage apparatus of a computer system is provided. The method can be embodied in a computer system comprising a computer having a variable length data format interface, and a storage apparatus which stores data on a recording media in a fixed block length format, for example. The storage apparatus is connected with the computer by the variable length data format interface. The method comprises a variety of steps, such as generating at the computer, parameters for transferring data recorded on the recording media, and generating at the computer an access command. The access command can include information indicating that data in fixed block length format is to be accessed. The access command can be in accordance with variable length data format. The method also includes transferring the access command from the computer to the storage apparatus through the variable length data format interface. Further, analyzing at the storage apparatus, the access command received from the computer; and accessing data recorded in fixed block length format based on the parameters if the access command received from the computer contains the information indicating that the access command is for the data recorded in fixed block length format can also be part of the method.
In a representative embodiment according to the present invention, a computer system is provided. The computer system comprises a first computer having a first interface for exchanging data in a variable length data format, a second interface for exchanging data in a fixed block length format, and a storage apparatus connected to the first computer by the first interface. The storage apparatus is capable of exchanging data with the first computer via the first interface according to a variable length data format. The first computer further comprises a parameter generator that generates parameters for transferring data recorded on a recording media of the storage apparatus according to a fixed block length format. The first computer can also comprise a command generator for generating a command according to a variable length data format. The command contains information indicating that data is to be accessed in fixed block length format, for example.
The storage apparatus can comprise a command analyzer for analyzing a command transferred by the first computer through the first interface. The command analyzer is operative to distinguish if a command transferred by the first computer is for data stored in accordance with fixed block length format or not. The storage apparatus can further comprise a transfer module for transferring data between the first computer and the storage apparatus according to a protocol of the first interface. The data is recorded or stored in a fixed block length format when the command transferred from the first computer is determined by the command analyzer to be a command in which the data is recorded or stored in fixed block length format.
In a yet further representative embodiment according to the present invention, a storage apparatus is provided. The storage apparatus can include a first interface in accordance with variable length data format and a second interface in accordance with fixed block length format; for example. A storage unit that stores data used by a computer connected by either of the first or second interface can also be part of the storage apparatus. Further, the storage apparatus can comprise a command analyzer for analyzing a command transferred by a first computer through the first interface. The command analyzer distinguishes if a command transferred by the first computer is directed to data stored in the storage unit in accordance with fixed block length format or not. Yet further, the storage apparatus can comprise a data transfer module for transferring data between the first computer and the storage apparatus using a protocol in accordance with the first interface. The data is read out from the storage unit or is written into the storage unit in fixed block length format, provided that when the command is transferred from the first computer, it is determined by the command analyzer to be a command to access data recorded in fixed block length format.
Numerous benefits are achieved by way of the present invention over conventional techniques. The present invention can increase data transfer performance in embodiments wherein the computers connected with CKD format interfaces read or write data stored in Fixed-Block Length format in disk subsystems. Further, in some embodiments, data can be shared between hosts at high speed. Further, specific embodiments according to the present invention can achieve effective data backup and data restoration between hosts with different interface formats.